The NFL strengthened its concussion protocol this offseason and added a third set of eyes at each game to specifically monitor the TV broadcast for signs of concussions. But the new system still seemed to fail Patriots safety Patrick Chung.

An NFL spokesman told the Globe Tuesday, “A joint review by the NFL and NFLPA of the application of the Concussion Protocol regarding New England safety Patrick Chung during the Patriots-Jaguars game is underway.”

Chung, the Patriots’ strong safety, didn’t play in the second half of Sunday’s 31-20 loss to the Jaguars in Jacksonville, Fla., after he was diagnosed with a concussion at halftime. Yet Chung appeared to suffer the injury early in the second quarter, and after leaving the game for one snap, he returned and played 14 defensive snaps plus two on special teams.

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The CBS game feed provided some evidence that Chung may have suffered a head injury, but neither of the two concussion spotters in the press box, nor the unaffiliated neurotrauma consultant watching the broadcast, ordered that Chung be checked for a concussion.

It wasn’t until after halftime, when Chung didn’t come out of the locker room with his teammates, that it was announced he had a concussion and would be out for the rest of the game.

The degree of Chung’s concussion is unclear, and Patriots coach Bill Belichick had no update on him when asked during a Tuesday morning conference call. The Patriots don’t return to the practice field until Wednesday.

Belichick said he didn’t know whether Chung was checked for a concussion during the second quarter because he was too busy coaching the game.

“I don’t know whether they did or didn’t,” said Belichick. “Those are medical procedures, and some of that is dictated by things from upstairs from the neutral physician and then that goes to our medical department.

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“I’m trying to coach the game. I don’t have time for a conversation with those guys. If the player is cleared, he’s cleared. If he’s not cleared, then he’s not cleared.”

Chung took a hit to his facemask from Jaguars tight end Niles Paul on a 1-yard run by Corey Grant with about 12:45 left in the second quarter.

The CBS broadcast showed Chung remaining on the ground for a couple of seconds after the play, grabbing his helmet.

While Nate Ebner replaced Chung on the next snap, the CBS broadcast briefly showed Patriots team doctor Mark Price speaking with Chung on the sideline and patting him on the back.

Chung returned for the next play.

Belichick said he was never told in the second quarter that Chung wasn’t medically cleared to play. He also doesn’t know whether Chung was checked for a concussion.

“That’s really a medical question that I can’t answer,” he said. “I don’t talk to the NFL medical people [at the game]. I’m never in communication with them at all. Never.”

This past offseason, the NFL strengthened its concussion protocol to avoid this type of situation, adding a third unaffiliated neurotrauma consultant (UNC) to each game after Houston quarterback Tom Savage suffered a vicious concussion last December that went unnoticed.

This UNC, a neurosurgeon or neurologist, sits in the press box and monitors the game broadcast to look for signs of concussions. The UNC sits next to two concussion spotters in the press box, who can stop the game if they see signs of a concussion, plus a video technician watching the video feed.

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“The idea is giving them sort of the 30,000-foot view of the field,” NFL medical director Dr. Allen Sills told the Globe in February. “Just remember, in real time, the docs on the sideline are trying to examine the player. The doc on the sideline doesn’t just sit there and stare at the monitor for 20 minutes. It’s very hard to see a lot of this stuff in real time, and even some of the replays are not that helpful for what you really want to see.”

In addition, players sometimes try to hide their concussion symptoms, and symptoms can often take several minutes to appear. But the concussion protocol is designed to protect against some of that.

Each sideline has a UNC, as well, and every NFL game has approximately 30 medical personnel on hand.

Yet Chung’s concussion Sunday apparently slipped by everyone in the stadium until halftime.

An All-22 video review of the hit appears to show Paul’s right shoulder slamming into Chung’s facemask. Paul and Patriots defensive tackle Danny Shelton then fell on top of Chung and drove him into the ground.

Chung didn’t take any other noteworthy hits in the 16 total snaps he played after returning, and didn’t show any obvious signs of concussion. He blitzed quarterback Blake Bortles four times, defended one run, and otherwise played in pass coverage, allowing a touchdown to Austin Sefarian-Jenkins (Chung was picked on the play).

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Chung also was back to return a punt two plays after taking the Paul hit, and was in on the Jaguars’ extra-point attempt with nine seconds left in the half.